Numerous baffling devices of the above type are already known. They force the coolant, which arrives under a core support plate through the annular gap which separates the casing from a pressure vessel, to flow through the fuel assemblies forming the core. In present day pressurized water reactors for example, the baffling device occupies the gap between the prismatic shape, with right angle facets, and the cylindrical casing.
In most baffling devices existing at the present time, the vertical baffling plates or "baffles" are held in position by horizontal plates, called formers. The mounting of such a baffling device, which must comply with strict dimensional requirements and withstand the temperature, radiation and differential pressure conditions prevailing in the vicinity of the core, raises problems which are only partially solved at the present time. In particular, the assembly of the plates and of the formers in the reactor, using screws whose number largely exceeds one thousand, is long and difficult. The breakage of a screw opens a gap, and so a leak jet harmful for the fuel rods of the assemblies placed in the vicinity.